The thermal journey that a temperature sensitive product takes, along the logistics trail from manufacturer to customer, is known as the “Cold Chain”. It is along this trail that vaccines can be exposed to thermal conditions that are deleterious or even destructive to their intended use of protecting lives.
Many devices have been developed to measure the thermal history of products along the “Cold Chain”. Some are expensive electronic recorders, others are inexpensive indicators, and some attempt to give an indication of the mean kinetic temperature of the products exposure experience.
Freeze-thaw indicators are known. For example, U.S. Pat. No. 4,163,427 discloses an apparatus in which melting ice is used to activate a dye formation in producing a color indication of thawing. A related invention uses a pigment rather than a dye to indicate a transition over the threshold temperature. U.S. Pat. Nos. 6,694,913 and 7,011,037 are directed to changed condition indicators. U.S. Pat. No. 7,770,534 is directed to a system and method for indication of temperature exposures beyond a set of predetermined limits that employs the salts of weak acid-strong base or of a strong acid-weak base compound as reactants. U.S. Pat. No. 8,957,780 is directed to a system for remotely monitoring changes in condition by measuring conductivity changes to solutions and/or emulsions together with color changes.
In the transfer or storage of many commercial products, such as vaccines, it is desirable to have some manner of indicating whether items that require freezer temperatures for stability, activity or the like have previously been thawed. Similarly, it is desirable to know whether a material that is stored frozen is allowed to thaw and subsequently is refrozen. Furthermore, it is desirable to know whether a material has been cooled below and then heated above a threshold temperature other than a freezing temperature (i.e., above or below the freezing temperature). Likewise it is desirable to indicate whether products have been subjected to high temperatures that might affect stability or activity.
It is desirable to provide a system including an indicator providing a thermal mass proxy for monitoring changes in condition.